This invention relates to a ball point pen cartridge including a source of pressure on the marking fluid or ink. More particularly, this invention relates to a ball point pen cartridge wherein the cartridge tube is sealed at the same time as pressure is applied to the ink in the tube.
Although the utilization of pressure within an ink cartridge so as to insure complete emptying of the ink and contact with the ball is well known, the various systems for accomplishing such pressurizing of the ink cartridge have not been completely successful. These prior marking implements utilize some type of hermetic sealing of the end of the cartridge opposite the marking point, such hermetic sealing often being a plug of rigid or elastic substance, Furthermore, the pressure exerted on the marking fluid or ink within the cartridge is often provided either by the reaction of a chemical compound within the cartridge subsequent to sealing or the vapor pressure of the gas of a liquified propellant type material. In these instances, the ball point marking instrument is permanently sealed under appropriate pressure; however, each of these types of marking implements utilizing a gas generating compound and hermetic sealing presents various difficulties as to functioning and manufacture.
In prior pressurized ball point pen ink cartridges, the gas generating or pressurized space at the rear of the cartridge is quite small and initially a relatively high pressure (preferably several atmospheres) is required. It is very important from the standpoint of long term stability that the pressure within this cartridge be maintained permanently. Since the amount of propellant or pressurant within the cartridge is quite small, any amount of leakage, no matter how small, could detrimentally effect the performance of the cartridge in view of the fact that the marking fluid itself is usually specially formulated for use with a pressurized type system.
Furthermore, the manufacture of these pressurized cartridges requires complex and sophisticated apparatus since the cartridge itself must be sealed while the same is pressurized or complex inserting apparatus or separating apparatus must be provided so as to maintain the various chemical reactants separate from each other until the desired time.
Also, the sealing of these cartridges has not been satisfactorily achieved since materials which are completely impermeable to gases are not sufficiently elastic to permit sufficient sealing of the marking instrument so as to ensure a permanent and absolute pressure seal. Furthermore, elastic materials which may easily be fitted into the cartridge tubes with adequate gas tightness are not completely impermeable to gases and the gases tend to escape through the sealing plug during storage. Also, these type processes do not allow for the mass production of implements having great uniformity since the pressure within individual cartridges may vary widely depending upon the tightness of the seal, the amount of pressurant inserted within the cartridge and the time lapse between pressurization and sealing.
The methods of sealing in such pressure hitherto known all involve dry joints between the cartridge tube and a plug which may be simple or of some complexity. Such dry joints, especially when mass-produced, do not assure with certainty perfect and permanent gas-tightness. In the case of joints involving metals, the slightest surface imperfection, for instance a microscopically small scratch on the inside wall of the cartridge at the location of the joint, or on the plug wall, will usually lead to leakage of the compressed gas which will ultimately render the cartridge unusable. Elastic materials suitable for such plugs are not entirely impermeable to gases and will therefor allow a gradual loss of pressure.